LED lighting device

ABSTRACT

Provided is a circuit for preventing an operating current of a TRIAC dimmer from being dropped below a holding current value. In this regard, a light emitting diode (LED) lighting device includes a TRIAC dimmer for controlling intensity of light emitted from an LED, a load connected between an output terminal of the TRIAC dimmer and a bridge rectifier to stabilize operation of the TRIAC dimmer even in low dimming level periods of the TRIAC dimmer, the bridge rectifier connected with the load to supply an operating current to the LED; and the LED for receiving the operating current from the bridge rectifier.

TECHNICAL FIELD

The present invention relates to a light emitting diode (LED) lightingdevice and, more particularly, to a circuit configuration capable ofpreventing flickering due to the characteristics of a triode foralternating current (TRIAC) dimmer.

BACKGROUND ART

Solid-state lighting (SSL) devices such as light emitting diode (LED)lighting devices attract much attention due to features such as lowpower consumption, long life and high luminance.

One of the significant elements of a lighting device is a dimmer forcontrolling the brightness of light, and recently TRIAC-based dimmersare frequently used (See Korean Patent No. 1055865).

In the above-described TRIAC-based dimmers, however, it is problematicthat the load of the LED lighting device is too small to appropriatelyoperate with the TRIAC dimmer. As such, the LED lighting device mayflicker at a very low diming level or may even get permanently switchedoff. That is, when TRIAC dimmers are present, low power consumption ofSSL devices may cause problems due to a latching and holding currents ofthe TRIAC dimmers.

In particular, lamps having low power consumption below 40 W (e.g., 2 Wcandle light bulb for E14 screw socket) do not reach the minimum load ofa TRIAC dimmer. Accordingly, an operating current of the TRIAC dimmerdrops below a holding current value and thus the LED lighting device mayflicker and even may stop working.

That is, the minimum dimming level (MIN) includes a range in which acurrent flowing through a TRIAC dimmer drops below a holding current,and LED lighting device flickers in these periods.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides an electric circuit capable of preventingan operating current of a TRIAC dimmer from dropping below a holdingcurrent value.

The present invention also provides an electric circuit capable ofstabilizing an output voltage of a TRIAC dimmer.

Other technical problems to be solved by the present invention will beunderstood by the following description of embodiments.

Technical Solution

According to an aspect of the present invention, there is provided alight emitting diode (LED) lighting device including an LED; a bridgerectifier; a TRIAC dimmer for controlling the luminance of the LED; anda load connected between an output terminal of the TRIAC dimmer and thebridge rectifier to stabilize the operation of the TRIAC dimmer even inlow dimming level of the TRIAC dimmer, wherein the bridge rectifier isconnected with the load to supply an operating current to the LED andthe LED receives the operating current from the bridge rectifier.

The load may include a load resistor that is connected between a firstnode of the output terminal and a second node of the output terminal,and connected in parallel with the bridge rectifier.

The load may include a first damping resistor that is connected betweena first node of the output terminal and a first node of the bridgerectifier, and a second damping resistor that is connected between asecond node of the output terminal and a second node of the bridgerectifier.

The load may include a first damping resistor that is connected betweena first node of the load resistor and a first node of the bridgerectifier, and a second damping resistor that is connected between asecond node of the load resistor and a second node of the bridgerectifier.

Each of the first and second damping resistors may include a pluralityof resistors connected in parallel with each other.

Advantageous Effects

According to the present invention, by adding a simple circuitconfiguration, an operating current of a TRIAC dimmer may be preventedfrom dropping below a holding current value in the minimum dimming levelof the dimmer, and thus flickering of a light emitting diode (LED) maybe prevented.

Furthermore, by adding damping resistors, an output voltage of the TRIACdimmer may be stabilized and thus operation of the LED may also bestabilized.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a TRIAC dimmer.

FIG. 2 is a block diagram of a light emitting diode (LED) lightingdevice according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of a load according to an embodiment of thepresent invention.

FIGS. 4 and 5 are graphs showing an operating current of a TRIAC dimmerin a dimming period, according to an embodiment of the presentinvention.

BEST MODE

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. The present invention may, however, be embodied inmany alternate forms and should not be construed as limited to theembodiments set forth herein. Accordingly, it should be understood thatthe invention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the claims.

Terms used herein to describe specific embodiments are for descriptivepurposes only and are not intended to limit the scope of the presentinvention. The singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

Hereinafter, the present invention will be described in detail byexplaining embodiments of the invention with reference to the attacheddrawings.

FIG. 1 is a circuit diagram of a TRIAC dimmer.

The basic elements of the TRIAC dimmer include a potentiometer R1, afixed resister R2, a capacitor C1, a variable resistor W1, a diode foralternating current (DIAC) and a TRIAC.

A resistor-capacitor (RC) network comprising R1, R2 and C1 delays thestart-up of the TRIAC until the voltage of C1 reaches a trigger voltageof the DIAC. When the resistance of the variable resistor W1 increases,the start-up delay that reduces the on-time or “conduction angle” of theTRIAC, increases.

The phase of the dimmer is controlled by W1 and C3, and the size of theconduction angle is controlled by a change of resistance of the variableresistor W1.

That is, when a current flowing through R2, R3 and W1 charges C3 and avoltage charged by the current reaches the break over voltage of theDIAC, a current is applied to a gate of the TRIAC, thereby turning onthe TRIAC. Accordingly, the conduction angle of the TRIAC is controlledby the current charged in C3.

The basic operation of the TRIAC dimmer will now be described withreference to FIG. 1.

When a current is applied to the gate of the TRIAC, the TRIAC isimmediately turned on and thus an operating current I of the dimmerflows. Here, the operating current I should not be dropped below aminimum holding current Ih to maintain the ON state of the TRIAC.

Accordingly, if the operating current I of the TRIAC dimmer drops belowthe holding current Ih, the TRIAC turns off. A current should be appliedto the gate to return the TRIAC to the ON state.

As such, the operating current I of the dimmer should always bemaintained not less than the holding current Ih to maintain theoperation of the TRIAC dimmer.

Here, the operating current I of the dimmer may be controlled by theload 10 that is applied to an output terminal of the dimmer.

FIG. 2 is a block diagram of a light emitting diode (LED) lightingdevice according to an embodiment of the present invention.

The LED lighting device comprising a TRIAC dimmer according anembodiment of to the present invention includes a TRIAC dimmer 100, aload 200, a bridge rectifier 300 and an LED 400.

The TRIAC dimmer 100 controls the brightness of or dims light. Thebrightness of light may be controlled by changing the value of theresistance of the variable resistor W1 described above with reference toFIG. 1.

The load 200 is connected between an output terminal of the TRIAC dimmer100 and the bridge rectifier 300. That is, the load 200 is connectedbetween node A and node C, and between node B and node D.

The circuit configuration of the load 200 will be described later withreference to FIG. 3.

The load 200 may stabilize the operation of the TRIAC dimmer 100 even ina low dimming level of the TRIAC dimmer 100. The reason why the load 200can stabilize the operation of the TRIAC dimmer 100 even in a lowdimming level of the TRIAC dimmer 100 will be described later withreference to FIG. 4.

The bridge rectifier 300 supplies a current to the LED 400. The bridgerectifier 300 receives an operating current from the TRIAC dimmer 100,rectifies the operating current, and supplies the rectified current tothe LED 400.

The LED 400 receives the current and emits light, and includes one ormore LEDs.

FIG. 3 is a circuit diagram of the load according to an embodiment ofthe present invention.

As described above with reference to FIG. 2, the load 200 is connectedbetween an output terminal (nodes A and B) of the TRIAC dimmer 100 andan input terminal (nodes C and D) of the bridge rectifier 300.

That is, the load 200 is connected in parallel with the bridge rectifier300 and is connected with the output terminal (nodes A and B) of theTRIAC dimmer 100.

The internal circuit configuration of the load 200 will be describedhereinafter.

The load 200 includes a load resistor 210 that is connected between afirst node (node A) of the output terminal of the TRIAC dimmer 100 and asecond node (node B) of the output terminal of the TRIAC dimmer 100, andis connected in parallel with the bridge rectifier 300.

Here, the bridge rectifier 300 and the LED 400 may be considered asloads having resistance. Accordingly, since the load resistor 210 isconnected in parallel with the bridge rectifier 300 and the LED 400, theresistance of the output terminal of the TRIAC dimmer 100 becomes low.

In addition, the load 200 may further include first damping resistors221 and 222 and second damping resistors 231 and 232. The first dampingresistors 221 and 222 are connected between the first node (node A) ofthe output terminal of the TRIAC dimmer 100 and a first node (node C) ofthe bridge rectifier 300, and the second damping resistors 231 and 232are connected between the second node (node B) of the output terminal ofthe TRIAC dimmer 100 and a second node (node D) of the bridge rectifier300.

The first damping resistors 221 and 222 and second damping resistors 231and 232 are configured to eliminate noise caused by overshoot orundershoot included in the waveform of a voltage output from the outputterminal of the TRIAC dimmer 100.

Here, each of the first damping resistors 221 and 222 and second dampingresistors 231 and 232 may include a plurality of resistors connected inparallel with each other.

Mode of the Invention

FIGS. 4 and 5 are graphs showing an operating current of a TRIAC dimmerin a dimming period, according to an embodiment of the presentinvention.

FIG. 4 is a graph showing the operating current of the TRIAC dimmer inthe dimming period when the load 200 is not configured.

A curved line indicates the operating current of the TRIAC dimmer, and adashed line indicates a holding current of the TRIAC dimmer.

As shown in FIG. 4, when the load 200 is not provided, the operatingcurrent of the TRIAC dimmer drops below the holding current of the TRIACdimmer in the minimum dimming level (MIN) of the dimming period.Accordingly, the TRIAC dimmer turns off in these ranges as describedabove with reference to FIG. 1.

FIG. 5 is a graph showing the operating current of the TRIAC dimmer inthe dimming period when the load 200 is provided.

FIG. 5 shows that, when the load 200 is provided, the operating currentof the TRIAC dimmer does not drop below the holding current of the TRIACdimmer in the minimum dimming level (MIN) of the dimming period.Accordingly, the TRIAC dimmer may maintain the ON state even in theseranges.

INDUSTRIAL APPLICABILITY

According to the present invention, by adding a simple circuitconfiguration, an operating current of a TRIAC dimmer may be preventedfrom dropping below a holding current in the minimum dimming level ofthe dimmer, and thus flickering of a light emitting diode (LED) may beprevented.

The invention claimed is:
 1. A light emitting diode (LED) lightingdevice comprising: an LED; a bridge rectifier; a TRIAC dimmer forcontrolling the luminance of the LED; and a load connected between anoutput terminal of the TRIAC dimmer and the bridge rectifier tostabilize the operation of the TRIAC dimmer even in low dimming level ofthe TRIAC dimmer, wherein the load includes: a first damping resistorthat is connected between a first node of the output terminal and afirst node of the bridge rectifier; and a second damping resistor thatis connected between a second node of the output terminal and a secondnode of the bridge rectifier, wherein the bridge rectifier is connectedwith the load to supply an operating current to the LED and the LEDreceives the operating current from the bridge rectifier.
 2. The LEDlighting device of claim 1, wherein the load includes a load resistorthat is connected between a first node of the output terminal and asecond node of the output terminal and is connected in parallel with thebridge rectifier.
 3. The LED lighting device of claim 1, wherein each ofthe first and second damping resistors comprises a plurality ofresistors connected in parallel with each other.
 4. A light emittingdiode (LED) lighting device comprising: an LED; a bridge rectifier; aTRIAC dimmer for controlling the luminance of the LED; and a loadconnected between an output terminal of the TRIAC dimmer and the bridgerectifier to stabilize the operation of the TRIAC dimmer even in lowdimming level of the TRIAC dimmer, wherein the load includes a loadresistor that is connected between a first node of the output terminaland a second node of the output terminal and is connected in parallelwith the bridge rectifier, wherein the load comprises: a first dampingresistor that is connected between a first node of the load resistor anda first node of the bridge rectifier; and a second damping resistor thatis connected between a second node of the load resistor and a secondnode of the bridge rectifier, wherein the bridge rectifier is connectedwith the load to supply an operating current to the LED and the LEDreceives the operating current from the bridge rectifier.
 5. The LEDlighting device of claim 4, wherein each of the first and second dampingresistors comprises a plurality of resistors connected in parallel witheach other.